There is that funny blond[?] dude from Wolf Guy, just remembered because some cr users were discussing about it. I had actually dropped that manga a year or 2 ago because of slow upload so i don't know if worse characters were introduced.

Hisoka of hunter x hunter (need I say why??)
millenium earl of d.gray-man (What the f*ck is with that grin?!)
Kurotsuchi Mayuri of Bleach (I hate his guts)
Katsura Kotonoha of school days (That 'head-in-her-bag' thing still bothers me today.)